When oxidizing organic saturated aliphatic aldehydes containing 5 to 9 carbon atoms to the corresponding monocarboxylic acids, an important objective is to obtain sufficiently high yields and product efficiencies at high enough conversion levels in a single pass, to avoid recycle of significant amounts of unreacted starting materials. Catalysts comprising copper and manganese facilitate this objective, since they result in the production of larger amounts of acid per pass than do manganese catalysts alone. However, a disadvantage often resulting from the use of copper-manganese catalysts in aldehyde oxidation processes, particularly ones in which the reaction product must be distilled to recover the desired product, is the plating out of copper in the distillation apparatus. Plating out, of course, can lead to undesirable mechanical problems, including erosion of reboilers and pump impellers and rapid pump seal failures.
Copending U.S. application Ser. No. 345,890 filed Feb. 4, 1982, assigned to Celanese Corporation claims a process of the type described utilizing a copper-manganese catalyst. This process provides commercially attractive high carbon efficiencies of aldehyde to acid at high aldehyde conversions. A single stage or two stage liquid phase reactor system generally gives sufficiently high aldehyde conversions so that recycle of unreacted aldehyde is, in most cases, unnecessary. However, when the reaction mixture is distilled to recover the acid, copper tends to precipitate and plate out on the distillation apparatus unless something is done to prevent it.
One means of overcoming this problem is to add relatively pure oxalic acid to precipitate copper and manganese from the reaction mixture as their oxalates, prior to the distillation step. This process is described in U.S. Pat. No. 4,289,708, issued Sept. 15, 1981 to Scott et al and assigned to Celanese Corporation. Copper and manganese can also be separated from the reaction mixture by precipitating them, again as their oxalates, by adding an aqueous oxalic acid solution. In this case, the manganese and copper oxalates precipitate into the aqueous phase, which can be readily separated from the organic acid product by decantation. The acid can then be further purified by distillation. However, aqueous oxalic acid cannot be used satisfactorily to treat mixtures containing valeric acid due to this acid's high solubility in water. This process is described in U.S. Pat. No. 4,246,185, issued Jan. 20, 1980 to Wood, Jr. and assigned to Celanese Corporation.
Copending application Ser. No. 466,447 assigned to the same assignee and filed concurrently with this application describes a process for extracting copper and manganese catalysts from a water-immiscible organic phase comprising a saturated aliphatic monocarboxylic acid containing 5 to 9 carbon atoms. The catalyst metal ions, copper and manganese, are reacted with aqueous formic acid to form the cupric and manganous formates which are highly soluble in water and have a low solubility in the water-immiscible organic phase comprising C.sub.5 -C.sub.9 saturated aliphatic monocarboxylic acid. Since valeric acid is very soluble in water, valeric acid containing manganese and copper can be combined with a water-immiscible organic solvent such as hexene and/or heptene to form a water-immiscible organic phase containing valeric acid in the presence of water. On the addition of aqueous formic acid to the organic phase containing the valeric acid, manganese and copper ions, manganous and cupric formates being highly soluble in water will form and be removed from the organic phase into the aqueous phase. C.sub.6 -C.sub.9 saturated aliphatic monocarboxylic acids are immiscible in water and will form the organic phase without additional organic solvents. Two phases, an organic phase and an aqueous phase, are formed. The organic phase comprising the monocarboxylic acid, is substantially free of copper and manganese and the acids can be separated from the aqueous phase. The C.sub.5 -C.sub.9 saturated aliphatic monocarboxylic acid can then be purified and readily recovered by distillation. However, the invention claimed in this application does not include the recovery of copper and manganese from the aqueous phase.
It is the purpose of this invention to recover the copper and manganese metals from the aqueous phase in the form of cupric and manganous alkanoates containing 5 to 9 carbon atoms. These alkanoates, in combination, can be used as oxidation catalysts and especially in the production of C.sub.5 -C.sub.9 saturated aliphatic monocarboxylic acids by the oxidation of their corresponding aldehydes.